The present invention relates to a slurry for planarizing metals by chemical-mechanical polishing (CMP) with improved planarity. The present invention is applicable to manufacturing high speed integrated circuits having submicron design features and high conductivity interconnect structures with high production throughput.
The escalating requirements for high density and performance associated with ultra large scale integration semiconductor wiring require responsive changes in interconnection technology. Such escalating requirements have been found difficult to satisfy in terms of providing a low RC (resistance and capacitance) interconnect pattern, particularly wherein submicron vias, contacts and trenches have high aspect ratios imposed by miniaturization.
Conventional semiconductor devices comprise a semiconductor substrate, typically doped monocrystalline silicon, and a plurality of sequentially formed dielectric interlayers and conductive patterns. An integrated circuit is formed containing a plurality of conductive patterns comprising conductive lines separated by interwiring spacings, and a plurality of interconnect lines, such as bus lines, bit lines, word lines and logic interconnect lines. Typically, the conductive patterns on different layers, i.e., upper and lower layers, are electrically connected by a conductive plug filling a via hole, while a conductive plug filling a contact hole establishes electrical contact with an active region on a semiconductor substrate, such as a source/drain region. Conductive lines are formed in trenches which typically extend substantially horizontal with respect to the semiconductor substrate. Semiconductor xe2x80x9cchipsxe2x80x9d comprising five or more levels of metallization are becoming more prevalent as device geometries shrink to submicron levels.
A conductive plug filling a via hole is typically formed by depositing an interlayer dielectric on a conductive layer comprising at least one conductive pattern, forming an opening through the interlayer dielectric by conventional photolitographic and etching techniques, and filling the opening with a conductive material, such as tungsten (W). Excess conductive material on the surface of the dielectric interlayer is typically removed by CMP. One such method is known as damascene and basically involves forming an opening in the interlayer dielectric and filling the opening with a metal. Dual damascene techniques involve forming an opening comprising a lower contact or via hole section in communication with an upper trench section. The entire opening is filled with a conductive material, typically a metal, to simultaneously form a conductive plug in electrical contact with a conductive line.
Cu and Cu alloys have received considerable attention as a candidate for replacing Al in interconnect metallizations. Cu has improved electrical properties vis-à-vis W, making Cu a desirable metal for use as a conductive plug as well as conductive wiring.
An approach to forming Cu plugs and wiring comprises the use of damascene structures employing CMP, as in Teong, U.S. Pat. No. 5,693,563. However, due to Cu diffusion through interdielectric layer materials, such as silicon dioxide, Cu interconnect structures must be encapsulated by a diffusion barrier layer. Typical diffusion barrier metals include tantalum (Ta), tantalum nitride (TaN), titanium nitride (TiN), titanium-tungsten (TiW), tungsten (W), tungsten nitride (WN), titanium-titanium nitride (Tixe2x80x94TiN), titanium silicon nitride (TiSiN), tungsten silicon nitride (WSiN), tantalum silicon nitride (TaSiN), and silicon nitride (SiN), for encapsulating Cu. The use of such barrier materials to encapsulate Cu is not limited to the interface between Cu and the dielectric interlayer, but includes interfaces with other metals as well.
In conventional CMP techniques, a wafer carrier assembly is rotated in contact with a polishing pad which is mounted on a CMP apparatus. The polishing pad is mounted on a rotating turntable or platen driven by an external driving force. The wafers are typically mounted on a carrier or polishing head which provides a controllable force, i.e., pressure, urging the wafers against the rotating polishing pad. Thus, the CMP apparatus effects polishing or rubbing movement between the surface of each thin semiconductor wafer and the polishing pad while dispersing a polishing slurry containing abrasive particles in a reactive solution to effect both chemical activity and mechanical activity while applying a force between the wafer and a polishing pad.
Conventional polishing pads employed in abrasive slurry processing typically comprise a grooved porous polymeric surface, such as polyurethane, and the abrasive slurry varied in accordance with the particular material undergoing CMP. Basically, the abrasive slurry is impregnated into the pores of the polymeric surface while the grooves convey the abrasive slurry to the wafer undergoing CMP. A polishing pad for use in CMP slurry processing is disclosed by Krywanczyk et al. in U.S. Pat. No. 5,842,910. Typical CMP is performed not only on a silicon wafer itself, but on various dielectric layers, such as silicon oxide, conductive layers, such as aluminum and copper, or a layer containing both conductive and dielectric materials as in damascene processing.
A distinctly different type of abrasive article from the above-mentioned abrasive slurry-type polishing pad is a fixed abrasive article, e.g., fixed abrasive polishing pad. Such a fixed abrasive article typically comprises a backing sheet with a plurality of geometric abrasive composite elements adhered thereto. The abrasive particles in a binder, e.g., a polymeric binder. During CMP employing a fixed abrasive article, the substrate or wafer undergoing CMP wears away the fixed abrasive elements thereby releasing the abrasive particles. Accordingly, during CMP employing a fixed abrasive article, a chemical agent is dispersed to provide the chemical activity, while the mechanical activity is provided by the fixed abrasive elements and abrasive particles released therefrom by abrasion with the substrate undergoing CMP. Thus, such fixed abrasive articles do not require the use of a slurry containing loose abrasive particles and advantageously reduce effluent treatment and dishing as compared to polishing pads that require an abrasive slurry. During CMP employing a fixed abrasive polishing pad, a chemical agent is applied to the pad, the agent depending upon the particular material or materials undergoing CMP. However, the chemical agent does not contain abrasive particles as in abrasive slurry-type CMP operations. Fixed abrasive articles are disclosed by Rugherford et al. in U.S. Pat. No. 5,692,950, Calhoun in U.S. Pat. No. 5,820,450, Haas et al. in U.S. Pat. No. 5,453,312 and Hibbard et al. in U.S. Pat. No. 5,454,844.
Fixed abrasive elements of conventional slurry-less type polishing pads are typically formed in various xe2x80x9cpositivexe2x80x9d geometric configurations, such as a cylindrical, cubical, truncated cylindrical, and truncated pyramidal shapes, as disclosed by Calhoun in U.S. Pat. No. 5,820,450. Conventional fixed abrasive articles also comprise xe2x80x9cnegativexe2x80x9d abrasive elements, such as disclosed by Ravipati et al. in U.S. Pat. No. 5,014,468.
In applying conventional planarization techniques, such as CMP, to Cu, it is extremely difficult to achieve a high degree surface uniformity, particularly across a surface extending from a dense array of Cu features, e.g., Cu lines, bordered by an open field. A dense array of metal (Cu) features is typically formed in an interlayer dielectric, such as a silicon oxide layer, by a damascene technique wherein trenches are initially formed. A barrier layer, such as a Ta-containing layer e.g., Ta, TaN, is then deposited lining the trenches and on the upper surface of the silicon oxide interlayer dielectric. Cu or a Cu alloy is then deposited, as by electroplating, electroless plating, physical vapor deposition (PVD) at a temperature of about 50xc2x0 C. to about 150xc2x0 C. or chemical vapor deposition (CVD) at a temperature under about 200xc2x0 C., typically at a thickness of about 8,000 A to about 18,000 A. In planarizing the wafer surface after copper metallization, erosion and dishing are typically encountered, thereby decreasing the degree of surface uniformity or planarity and challenging the depth of focus limitations of conventional photolitographic techniques, particular with respect to achieving submicron dimensions, such as below about 0.25 micron.
Conventional techniques for CMP Cu and Cu alloys exhibit unacceptably low polishing rates or poor polishing results. Conventional CMP slurries for Cu and Cu alloys contain abrasive particles, such as alumina or silica, an oxidizer, such as hydrogen peroxide or an acid, a complexing agent and an inhibitor, such as benzotriazole. EPO 864 742 A2, discloses a CMP slurry for Cu and Cu alloys containing a urea hydrogen peroxide oxidizer, a complexing agent, such as ammonium oxalate or tartaric acid, an abrasive, a film forming agent, e.g., benzotriazole, and an optional surfactant. The conventional CMP operates by oxidizing the surface of the metal which is then abraded by the abrasive particles. In EPO 846 742 A2, the complexing agent disturbs the passivation layer during mechanical abrasion and forms a complex with the oxidized metal thereby limiting the depth of oxidation.
Conventional oxidizers are small organic molecules, such as hydrogen peroxide, ferric nitrate, potassium iodate and ammonium persulfate. The oxidizers tend to form a thin oxide film to stop further etching once an oxide film is formed. However, the use of small oxidizing molecules tends to diffuse to the metal/oxide interface, or simply diffuses through the less dense oxide film due to their small size and affinity for the metal surface. Such overetching of metal lines results in dishing which may form capillary forces to suck the aqueous solution thereby exacerbating dishing. Currently, dishing is a significant problem in CMP of metal layers, particularly Cu and Cu alloys.
There exists a need for a CMP slurry and methodology for planarizing metals with reduced dishing. There exists a particular need for a CMP slurry for planarizing Cu and Cu metal alloy layers with reduce dishing, increased surface planarity, increased throughput and reduced manufacturing costs.
An aspect of the present invention is a CMP slurry for planarizing metals, such as Cu and Cu alloys, at high production throughput with no or significantly reduced dishing, improved surface planarity, increased throughput and reduced manufacturing costs.
Additional aspects and other features of the present invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The aspects of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other aspects are implemented in part by a slurry for chemical-mechanical polishing a metal, the slurry comprising a reagent having: a first moiety for oxidizing the metal and for complexing with the metal and/or metal oxide; and a second moiety for minimizing overetching the metal.
Another aspect of the present invention is a method of planarizing a surface of a metal by chemical-mechanical polishing employing a slurry comprising a reagent having: a first moiety for oxidizing the metal and for complexing with the metal and/or metal oxide; and a second moiety for minimizing overetching the metal.
Embodiments of the present invention comprise CMP Cu or a Cu alloy employing a slurry containing an oxidizing moiety and a complexing moiety, wherein the reduced form of the oxidizing moiety comprises a complexing agent for the metal. Embodiments of the present invention include reagents which are peroxy acids, such as peroxybenzoic acid, chloroperoxybenzoic acid, peroxyacetic acid, and peroxyformic acid. Embodiments of the present invention further include polyethylene glycol peroxy acids.
A further aspect of the present invention is a slurry for chemical mechanical polishing and metal, the slurry consisting essentially of: an amine-peroxy acid; abrasive particles; an inhibitor and deionized water.
Another aspect of the present invention is a method of planarizing a surface of a metal by chemical mechanical polishing employing a slurry consisting essentially of an amine-peroxy acid; abrasive particles; an inhibitor; and deionized water.
Embodiments include employing urea hydrogen peroxide as the amine-peroxy acid which advantageously dissociates in water into an oxidizing agent and complexing agent, thereby avoiding the necessity of providing a separate complexing agent and enhancing the shelf life of the oxidizing component.
Additional aspects of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein embodiments of the present invention are described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.